Investigating species-level flammability across five biomes in the Eastern Cape, South Africa

• Using standardised experimental methods, we assess the flammability of 99 species from five major South African biomes.
• Fire-prone Grassland and Fynbos have the greatest proportion of highly flammable species.
• Fire-free Forest, Nama-Karoo and Thicket have the lowest proportion.
• Nonetheless, fire-free biomes have a surprisingly high number of highly flammable species.
• No current theory encompasses the observed flammability at the species level.

The causes and consequences of plant flammability are a contested issue. In fire-prone ecosystems, high flammability is invoked as a trait (in combination with fire-survival traits) that enhances reproductive success and reduces competition in the post-fire environment. On the other hand, flammability may be a consequence of other selective forces, for example, deterring herbivores. Here, we use a standardised method for estimating the flammabilities of 99 species distributed across five biomes in a small area of the southwestern Cape Floristic Region, South Africa. The fire-prone Fynbos and Grassland biomes included many highly flammable species, notably among graminoids and small-leaved shrubs with densely packed, fine twigs. However, Fynbos included many weakly flammable species. In the fire-free biomes (Forest, Nama-Karoo and Thicket), most species had low flammability, especially succulents. However, flammable species also occurred in all three biomes, including species with traits normally attributed to non-flammable species (e.g. large leaves sparsely arranged on coarse twigs). Since these biomes are fire-free, flammability in these species cannot be attributed to a fire-related selective regime.